Switching type regulated output voltage power supply



June 6, 1967 K. KUPFERBERG ETAL SWITCHING TYPE REGULATED OUTPUT VOLTAGEPOWER SUPPLY Original Filed Jan. 6, 1960 2 Sheecs -Sheet' 1 19 j 78 l lI so i I H: 33

is L"! F|G.l 70, AMP

SWITCH CONTROL V (OUT) l1 (ouT) I I (MAX) LIMIT INVENTOR. KENNETHKUPFERBERG AARON ROSENFELD ATTORNEYS FIG. 2A

June 1957 K KUPFERBERG ETAL 3,3

SWITCHING TYPE REGULATED OUTPUT VOLTAGE POWER SUPPLY Original Filed Jan.6, 1960 2 Shee ts-Sheet Q INVENTOR KENNETH KUPFERBERG F|(; 4 AARON'ROSENFELD BYWMMM ATTORNEY United States Patent 3,324,378 SWITCHENG TYPEREGULATED OUTPUT VULTAGE POWER SUPPLY Kenneth Kupferberg, Flushing, andAaron Rosenfeld,

Jackson Heights, N.Y., assignors to Forhro Design Inc., New York, N.Y.,a corporation of New York Continuation of application Ser. No. 823, Jan.6, 1960.

This application June 17, 1963, Ser. No. 292,811

7 Claims. (Cl. 321-18) This application is a continuation of copendingapplication entitled, Switching Type Regulated Output Voltage PowerSupply, filed on Jan. 6, 1960, and bearing Ser. No. 823.

This invention relates to regulated output voltage power supplies and,more particularly, to a power supply of this type incorporating a novelswitching circuit for control of the output voltage within very closelimits.

There are various known types of power supplies having regulated outputvoltages, and the type used in any particular instance will dependlargely on such factors as the input power supply, the desired powercapacity, the desired output voltage, and the desired sensitivity ofresponse, among other factors. These known power supplies may beclassified as to whether they are energy dissipating or energynon-dissipating. They may also be classified as to speed of response andas to Whether they can operable on AC. or D.C.

The non-dissipating types include the motor variac" and magamp ormagnetic amplifier voltage regulators. A typical motor variac typeoperates on AC, and has a response time of one second, an output voltageof 115 volts AC, and a capacity of 5 kva. The magnetic amplifier type ofcontrol operates on AC. and has a response time of to 100 milliseconds,a typical output power might be 28 volts D.C. at 50 amperes.

The dissipating types of voltage regulators include series electronictube regulators and series transistor regulators. The series tube typeof regulator operates on D.C. and has a fast response of about 50microseconds, a typical output power of 300* volts D.C. at 500millamperes. The series or pass transistor type of regulator alsoopcrates on D.C. and has a fast response time of as low as 50microseconds, a typical output power of 28 volts D.C. at 10 amperes.

This circuit triggers a cascaded transistor amplifier which, in turn,triggers the pass transistor to become fully conductive or substantiallynon-conductive, depending upon the relative variation in the loadvoltage. For example, if the output voltage drops, the pass transistorremains fully conductive until the condenser voltage attains a valueslightly above the desired value. Conversely, if the output voltagerises, the pass transistor remains substantially non-conductive untilthe output voltage drops slightly below the desired value.

Consequently, the condenser voltage is maintained at the desired valuewithin close limits. There is very low power loss because, when the passtransistor is fully conductive, the transistor voltage drop is verysmall and when the pass transistor is substantially non-conductive,there is a potential thereacross but substantially no courrent fiowtherethrough. Due to the absence of any inductive components in thecontrol circuitry, the opening and closing of the pass transistor switchis substantially instantaneous.

For an understanding of the invention principles, reference is made tothe following description of a typical embodiment thereof as illustratedin the accompanying drawings. 7

In the drawings:

FIG. 1 is a schematic block diagram of a switching voltage regulatorembodying the invention;

3,324,378 Patented June 6, 1967 FIG. 2 is a graph illustrating thevoltage regulation characteristic;

FIG. 2A is a graph of the current from a suitable current limitedsource;

FIG. 3 is a voltage-current curve of the sistor;

FIG. 4 is a schematic wiring diagram corresponding to FIG. 1.

The same effect can be attained by using a variable resistance in serieswith the condenser, in place of the switch and varying such resistanceto maintain the condenser potential within close limits. However, such avariable resistance will consume power at all times, whereas the switchdoes not. Such a variable resistance could be a rheostat, a spacedischarge device, or a transistor, all of which, however, dissipatepower when used in such application.

In accordance with the present invention, a transistor is used as aswitch in series between a substantially current limited supply and acondenser which may be connected to a load resistance in paralleltherewith during use of the power supply. Novel circuitry is provided totrigger this pass transistor between fully conductive and substantiallynon-conductive states. More particularly, the load voltage measuringnetwork is connected in a reference bridge, which may be a standardizedor a plug-in type, including a source of fixed references potential andadjustable resistance means. Details concerning the operation of such areference bridge are set forth in United States Patent No. 3,028,538issued on Apr. 3, 1962.

This latter means is adjusted to a value corresponding to the desiredoutput voltage. The network or bridge has a transistorized control orcomparison amplifier connected thereacross in such manner that anyvariation in the voltages drop across the output terminals from thedesired value is detected as to relative direction or polarity by thecomparison amplifier. This variation is then suitably amplified by atransistor amplifier and used to trigger a pass tran- .bi-stablemultivibrator, such as a Schmitt trigger, unijunction transistor, etc.

From this it will be noted that the non-dissipating types of controlshave a higher output capacity but a slower response time than thedissipating types. On the other hand, the dissipating types of controlare characterized by a much faster response time but a lower outputcapacity. Additionally, the energy dissipating types have lowerefiiciency.

A highly desirable power supply having a regulated output voltage wouldbe one combining the advantages of both types without the disadvantagesof either. For example, such a supply would be substantiallynon-dissipating, have a response time at least as fast as that of thebest dissipating type, and an output capacity at least equal to that ofthe non-dissipating type.

If a condenser is connected by a series switch to a constant currentsupply, the condenser will charge as long as the switch is closed. Also,there is substantially no voltage drop across the switch. If now theswitch is opened, there is no current flow although there exists apotential across the open switch. The condenser remains charged to thevoltage attained at the instant the switch was opened provided there isno load resistance connected across the condenser.

If a load resistor is connected in parallel with the condenser, however,the condenser will discharge through the resistor so that the potentialacross the condenser will decrease. By re-closing the switch, thecondenser will recharge toward a potential determined by the controlcircuitry. Hence, through operation of the switch by the controlcircuitry, it is possible to regulate the voltage across the condenserwithin very close limits.

Referring to FIG. 1, a current limited source is provided comprising aflux-oscillating transformer 7881 with line input connecting terminals79 and 80 and oscillation tuning capacitor 82. A suitable output voltageis taken from lead 84 and tap 83 which is applied to a suitablerectifier such as bridge 85-66-8748 and providing filtered directcurrent across capacitor 89' at points 11 and 12. The flux-oscillatingtransformer 78451 has the well-known current limited characteristic asshown in FIG. 2A and thus, the rectified current at terminals 11-12 willhave this same current limited characteristic and, as far as the balanceof the circuit is concerned, may be considered a current limited source.This current limited source has been enclosed by a dash line anddesignated as current limited source 10. This current limited source, ashas been pointed out above, provides part of a highly efiicientregulated power supply, since it is not necessary to provide the morecomplex and costly constant current type of source.

Referring again to FIG. 1, current limited source has its negativeterminal connected to the collector 21 of a pass transistor 20. Emitter22 of transistor 20 is connected to a junction point 31 of a referencenetwork 'or bridge 30, and the positive terminal of source 10 isconnected to junction point 34 of network 30. Junction points 31 and 34are respectively connected to load or output terminals 24, 26 acrosswhich is connected a load schematically represented by resistance 25. Inaccordance with the invention, a relatively high capacity condenser isconnectedin parallel with output or load terminals 24, 26 and is chargedfrom source 10 through transistor acting as a switch. Condenser 15supplies the load or output voltage to terminals 24, 26.

Bridge or network 30 has two otherjunction points, 32 and 33. A constantreference voltage source 35 is connected between points 31 and 32, and aresistance 36 is connected between points 32 and 33. An adjustableimpedance 37, used to set the output voltage at a desired pre-set value,is connected between points 33 and 34. A transistorized control orcomparison amplifier 40 is connected between points 31 and 33, and itsoutput is connected to a transistorized switching control 50 whichthrough a transistor amplifier 70, triggers pass transistor 20 betweenfully conductive and substantially non-conductive states.

In the operation of the arrangement thus far described, potentiometer orvariable resistance 37 is adjusted in accordance with desired outputvoltage. The design of network 30 is such that, when the voltage dropacross resistance is equal to such desired value, the series voltagedrops across components 25 and 37 will equal the series voltages acrosscomponents 35 and 36. There will thus be no potential difference betweenpoints 31 and 33, and thus no potential difference across comparisonamplifier 40.

Referring to FIG. 2, when the source 10 is connected to the system, passtransistor 20 is immediately triggered to the conductive state due tothe voltage across condenser 15 being zero, and thus less than thepre-set output voltage. The voltage across condenser 15 builds up, asindicatedby the steeply sloping portion A of the curve, until thecondenser voltage E-l exceeds the desired output voltage by a smallpredetermined amount. At this time, pass transistor 20 is triggered tothe substantially non-conductive state, and becomes an open switch.

If the load is drawing current, the condenser will slow-v ly dischargeas indicated at B until its voltage drops to the value E-2 which is avery small predetermined amount below the desired output voltage. Atthis voltage value, pass transistor 20 is triggered to the fullyconductive state to act as a closed switch. Condenser 15 quicklycharges, as indicated at C, to the voltage E-l, at which time transistor20 is triggered to the substantially nonconductive state to open theswitch. This action continues as long as the load, or resistance 25,draws current.

The voltage change responsive action results from the comparisonamplifier 40 detecting the polarity of any potential ditference betweenjunction points 31 and 33'. If the output voltage exceeds the pre-setvalue, point 31 becomes negative relative to point 33 and vice versa ifthe output voltage drops below the pre-set value. In the first case,amplifier 40 triggers the bi-stable multivibrator in switch control in adirection to supply a pulse which, when amplified by amplifier 70,triggers transistor 20 to the substantially non-conductive state. In thesecond case, transistor 29 is triggered, in a similar manner, to thefully conductive state.

Due to the pass transistor acting as an instantaneously opened or closedswitch, this transistor consumes little power. Referring to the voltageand current curves of FIG. 3, it will be noted that, when the transistoris fully conductive and current is flowing therethrough, the voltagedrop across the transistor approaches zero. When transistor 20 istriggered to the substantially non-conductive state, the voltage dropacross the transistor is equal to the difference between the voltage ofsource 10 and the voltage of condenser 15, but there is no current flowthrough the transistor 20. The only time the transistor 20 consumespower is during the short interval, nearly instantaneous, that thevoltage across the transistor is building up as the current is dropping,and vice versa. At all other times, either the voltage drop across thetransistor is low or the current flow therethrough is zero, and hencelittle power is consumed by the transistor.

Referring now to FIG. 4, which schematically illustrates a practicalembodiment of the switching regulator, the source of supply ispreferably a device, such as a flux oscillating transformer, whosecurrent output is substantially constant at its limiting value. Negativeterminal 11 of such source is connected through a resistance 13 tocollector 21 of transistor 20, and positive terminal 12 of the source isconnected to junction point 34. Emitter 22 is connected throughequalizing resistor 14 and ammeter 16 to junction point 31. The load oroutput terminals 24 and 26 are thus negative and positive respectively.A bleeder resistance 15' is connected in parallel with the seriesconnection of condenser 15 and ammeter '16.

In the network 30, the constant voltage reference could be a Zener diodeor any other suitable constant voltage device. Comparison amplifier 40comprises a PNP junction transistor 45A and an NPN junction transistor45B. Collector 41A and emitter 42B are connected through respectivelimiting resistors 44A, 44B, to the negative terminal 1'7 of a voltagesource, and emitter 42A and collector 41B are connected through a commonlimiting resistor 46 to the positive terminal 18 of such source. Emitter42A is connected to junction point 31, base 43A is connected to emitter42B, and base 43B is connected to junction point 33. The output ofamplifier 40 is taken from collector 41A by conductor 47 and applied tothe base 53 of a transistor amplifier 55 in switch control 50.

Collector 51 of transistor 55 is connected through resistor 54 topositive terminal 1 8, and emitter 52 is connected through resistor 56to negative terminal 17. Transistor 55 operates as a common emitteramplifier, and its collector 51 is connected to the base 63 of one of apair of transistors and 65 connected as a bi-stable multivibrator of theSchmitt trigger type. As will be understood by those skilled in the art,in a multivibrator of this type, when one transistor 60 is conductive,the other transistor is non-conductive, and vice versa. Collectors 61and 66 of transistors 60 and 65 are connected through resistors 64A and64B, and a common-resistor 69-, to negative terminal '17. Emitters 62and 67 are connected together and, through resistors 57 and '58, topositive terminal 18. Base 68 is connected through resistors 59 and 58to positive terminal 18.

The output of bi-stable .multivibrator 6065 is taken from collector 66by a conductor 71 and applied to the base of transistor 75A forming oneof three cascade emitter follower transistors incorporated in amplifier'70. The emitters of the three transistors are connected throughrespective resistors 72A, 72B, 72C to positive terminal 73 of a voltagesource. The collectors of transistors 75A and 75B are connected throughrespective resistors 76A, MB to negative terminal 74 of this source,while the collector of transistor 750 is connected to negative terminal11. It will be noted that the emitter of each transistor is connected tothe base of the next succeeding amplifier, with a conductor 77connecting the emitter of transistor 75C to base 23 of pass transistorswitch 20.

The switching regulator operates in the following manner. Assuming thatthe output voltage across junctions 31 and 34 tends to exceed thepre-set value, junction point 33 will become more positive causing thebase 43B of NPN transistor 45B to become more positive and causing thistransistor to conduct. When transistor 45B conducts, emitter 42B becomesmore positive. This causes base 43A of PNP transistor 45A to become morepositive, tending to cut off this transistor and thus reducing itscollector current. This reduces the voltage drop across resistor 44A, sothat collector 41A goes more negative.

Oorrespondingly, base 53 of transistor amplifier 55 goes more negative,resulting in its collector 51 going more positive due to the decrease incollector current and thus in the voltage drop across resistor 54. Theresultant more positive voltage on the base 63 of transistor 60 of thebistable multivibrator triggers this transistor to the non-conductivestate, which triggers transistor 65 to the conductive state. Withtransistor 65 conducting, the voltage drop across resistor 64B increasesso that collector 66 becomes more positive.

This more positive voltage is applied through conductor 71 to the baseof transistor 75A so that a positive voltage, as amplified by thecascade emitter follower transistors 75A, 75B and 75C appears at base 23of pass transistor 20 and triggers the pass transistor to thenon-conductive state to act as an open switch. The output or loadvoltage thereupon decreases. When the output voltage drops to the lowerlimit, point 33 becomes negative rela tive to point 31 and, in a manneranalogous to that described, pass transistor 20 is triggered to theconductive state to act as a closed switch.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventionprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. A regulated output voltage power supply comprising, in combination, acurrent limiting flux oscillating input transformer and rectifier meansconnected to said transformer for providing a source of DO. voltage tobe regulated; a pair of output terminals, adapted to supply a loadconnected therebetween; a pass transistor in series connecting saidsource to said terminals; a condenser in parallel with said terminals;said transistor, when conductive, charging said condenser from saidsource and said condenser, discharging through the load; switch controlmeans connected to said pass transistor and effective ,to trigger thelatter between fully conductive and substantially non-conductive states;and a comparison network, including said output terminals, an outputvoltage adjusting resistance, and a reference voltage source, and meansresponsive to the difference between said output voltage and saidadjustable reference voltage connected to control the operation of saidswitch control means to trigger said pass transistor to either of saidstates to act as an on-off switch to control charging of said condenserto maintain the output voltage within narrow pre-set limits.

2. A regulated output voltage power supply comprising, in combination, acurrent limiting flux oscillating input transformer and rectifier meansconnected to said transformer for providing a source of DC. voltage tobe regulated; a pair of output terminals, adapted to supply a loadconnected therebetween; a pass transistor in series connecting saidsource to said terminals; a condenser in parallel with said terminals;said transistor, when conductive, charging said condenser from saidsource and said condenser, when the transistor is non-conductive,discharging through the load; switch control means connected to saidpass transistor and effective to trigger the latter between fullyconductive and substantially nonconductive states; a comparison network,including said output terminals, an output voltage adjusting resistance,a source of reference potential, and an output voltage variationresponsive means, controlling operation of said switch control means totrigger said pass transistor to either of said states to act as anon-off switch to control charging of said condenser to maintain theoutput voltage within narrow pre-set limits.

3. A regulated output voltage power supply as claimed in claim 1including an amplifier, comprising plural cascade emitter followerconnected transistors, connecting said switch control means to said passtransistor.

4. A regulated output voltage power supply as claimed in claim 1 inwhich said switch control means comprises a bi-stable multivibrator.

5. A regulated output voltage power supply as claimed in claim 1 inwhich said switch control means is a Schmitt trigger circuit.

6. In a voltage regulated power supply, the combination of, a currentlimited source of direct current comprising a flux oscillatingtransformer, a pair of load terminals for receiving connections to anexternal load to be supplied with regulated voltage, a reference voltagesource, an adjustable reference voltage source derived from the firstsaid reference voltage source, connections between said load terminalsand said adjustable reference voltage source to compare one with theother and to provide two points across which appears any differencevoltage existing between the load voltage and the adjustable referencevoltage, a capacitor connected across said load terminals, a circuit forcharging said capacitor from said source of direct current including aseries connected pass transistor, and a circuit for charging saidcapacitor intermittently as long as the voltage across said load is lessthan the adjustable reference voltage including a comparison amplifierconnected across said two points and a transistor switching circuitconnected between said amplifier and said pass transistor to turn saidpass transistor substantially on and off to reduce said differencevoltage to substantially zero.

7. A voltage regulated power supply as set forth in claim 6 andincluding at least one emitter follower connected .transistor in seriesbetween said transistor switching circuit and said pass transistor.

References Cited UNITED STATES PATENTS 2,776,382 1/1957 Jensen 307-972,810,105 10/1957 Henrich 323-22 3,005,147 10/1961' Thomas 323-9 JOHN F.COUCH, Primary Examiner. K. D. MOORE, Assistant Examiner.

1. A REGULATED OUTPUT VOLTAGE POWER SUPPLY COMPRISING, IN COMBINATION, ACURRENT LIMITING FLUX OSCILLATING INPUT TRANSFORMER AND RECTIFIER MEANSCONNECTED TO SAID TRANSFORMER FOR PROVIDING A SOURCE OF D.C. VOL BEREGULATED; A PAIR OF OUTPUT TERMINALS, ADAPTED TO SUPPLY A LOADCONNECTED THEREBETWEEN; A PASS TRANSISTOR IN SERIES CONNECTING SAIDSOURCE TO SAID TERMINALS; A CONDENSER IN PARALLEL WITH SAID TERMINALS;SAID TRANSISTOR, WHEN CONDUCTIVE, CHARGING SAID CONDENSOR FROM SAIDSOURCE AND SAID CONDENSER, DISCHARGING THROUGH THE LOAD; SWITCH CONTROLMEANS CONNECTED TO SAID PASS TRANSISTOR AND EFFECTIVE TO TRIGGER THELATTER BETWEEN FULLY CONDUCTIVE AND SUBSTANTIALLY NON-CONDUCTIVE STATES;AND A COMPARISON NETWORK, INCLUDING SAID OUTPUT TERMINALS, AN OUTPUTVOLTAGE ADJUSTING RESISTANCE, AND A REFERENCE VOLTAGE SOURCE, AND MEANSRESPONSIVE TO THE DIFFERENCE BETWEEN SAID OUTPUT VOLTAGE AND SAIDADJUSTABLE REFERENCE VOLTAGE CONNECTED TO CONTROL THE OPERATION OF SAIDSWITCH CONTROL MEANS TO TRIGGER SAID PASS TRANSISTOR TO EITHER OF SAIDSTATES TO ACT AS AN "ON-OFF" SWITCH TO CONTROL CHARGING OF SAIDCONDENSER TO MAINTAIN THE OUTPUT VOLTAGE WITHIN NARROW PRE-SET LIMITS.